In ink-jet printing methods, droplets of ink are directly projected onto a recording medium from very fine nozzles and allowed to adhere to the recording medium to form characters and images. The ink-jet printing methods have been rapidly spread because of their various advantages such as easiness of full coloration, low costs, capability of using ordinary paper (plain paper, recycled paper) as the recording medium, non-contact with printed images and characters, etc.
Among such printing methods, in view of enhancing the weather resistance and water resistance of printed images and characters, an ink-jet printing method utilizing an ink containing a pigment as the colorant has now come to dominate.
WO 00/39226 discloses a water-based ink containing a pigment-containing vinyl polymer.
JP 8-157761A discloses a water-based ink containing an oil film-forming component which is prepared by dissolving a water-insoluble resin therein in order to suppress color bleeding. However, since the water-insoluble resin must be dissolved in the ink, a content of the water-insoluble resin in the ink is small, so that the resultant ink fails to exhibit a sufficient function.
JP 2003-183554A discloses an ink containing 10 to 1000 ppm of a phthalic diester and a latex in order to form images having a good gloss. However, since a content of the phthalic diester in the ink is small, the resultant ink fails to exhibit a sufficient function.
WO 99/52966 discloses a water-based pigment-containing dispersion composed of a carboxyl group-containing thermoplastic resin and a pigment dispersed therein, which is produced by crosslinking the carboxyl group-containing thermoplastic resin after dispersing the pigment therein. In WO 99/52966, it has been described that the thus produced water-based pigment-containing dispersion is excellent in light resistance, water resistance, solvent resistance, stability with time, etc.
JP 9-104834 discloses a process for producing a water-based pigment-containing dispersion by using a pigment and a resin containing a carboxyl group and a crosslinkable functional group, and reacting the crosslinkable functional group of the resin with a crosslinking agent for crosslinking the resin. In JP 9-104834, it has been described that the thus produced water-based pigment-containing dispersion has a good storage stability and is capable of forming a coating film having excellent water resistance and durability, etc.
However, the water-based inks containing the above pigment-containing dispersions have failed to satisfy a good gloss and a good storage stability.